There have been many patents issued and many papers published on the manufacture of lumber-like products from wood particles. Similarly it is common practice to manufacture waferboard-type panel products from wood particles and there have been a number of articles published.
In the realm of oriented strandboard, the normal practice has been to manufacture a board from particles having a maximum length of up to about 4 inches (100 mm) and many papers and articles have been published advocating 4 inches (100 mm) as a maximum length of wafer.
However, in the recently issued U.S. Pat. No. 4,610,913, issued Sept. 9, 1986 and of which this application is a continuation-in-part, advantages can be obtained utilizing long wafers in forming a layered waferboard product.
Australian patent No. 136,844 issued Mar. 28, 1950 is one of the earlier disclosures relating to the manufacture of lumber from particles. In this patent the particles recommended are sticks, twigs, etc that are oriented in the longitudinal direction of the lumber and secured together. It has also been proposed in Czechoslovakian patent number 93,154 issued Dec. 15, 1959 to Stofko, to produce a moulded product by orienting wood elements in what are broadly defined as profiles such as I, U, T, L and others including pipes and windows, and pressing to consolidate into a finished or semifinished product. The teachings of this patent are further applied by articles published by Stofko in Drevarsky Dyskum 2 No. 1:81-102 (1957); Drevarsky Dyskum 5 No 2:241-261 (1960); Drevarsky Dyskum 2:127-148 (1962) and Drvna Industriaja 21 (6):104-107 (1970). In these articles Stofko discusses panel products and lumber products presumably moulded as taught in his patent and emphasizes the importance of slenderness ratio, i.e. the ratio of length to thickness of the wood particles to obtain the desired structural properties at an acceptable density.
U.S. Pat. No. 3,164,511 issued Jan. 7, 1965 to Elmendorf discloses the manufacture of a lumber product from wafers having length of up to about 6 inches (150 mm), width up to about 1/4 inch (150 mm) and thicknesses between 0.005 to 0.02 inches (0.1 to 0.5 mm). To applicant's knowledge no commercial lumber products utilizing such wood particles have been manufactured and sold.
U.S. Pat. No. 3,956,555 issued May 11, 1976 to McKeen describes the manufacture of a laminated beam from a combination of oriented and random wood particles in a press by laying alternative strips of oriented and random particles and then consolidating under pressure to form a panel and splitting the oriented strips to divide the panel in to structures having end side sections that are oriented and would function similar to flanges of an I beam interconnected by a random oriented section that would function as the web of an I beam. This is a relatively complicated structure with limited strength and suitable only for use with the products oriented to be loaded perpendicular to the split faces.
As far as applicant is aware, the product described in U.S. Pat. No. 4,061,819 issued Dec. 6, 1977 to the present inventor describes the only commercially viable suitable lumber product formed from wood particles (strands). This patent teaches the use of relatively long strands to obtain structural products having physical characteristics including density and strength characteristics similar to, and in some cases better than, those of the natural wood product it replaces.
U.S. Pat. No. 4,122,236 issued Oct. 24, 1978 to Holman describes an artificial lumber product moulded from splinters having a length of the range of about 2 to 10 inches.
Generally when waferboards (panels) or the like are made, the density profile through the panel is such that the skins of the panel have maximum density and the core has the least density. Stated another way, the strength of the skins of the panel is higher than the strength of core, however, since panels are normally used with the core extending along the neutral axis of the bending moment such a density distribution is not a major factor in determining bending strength. It is known that the rate of pressure application in a press can be used to change the density profile through the thickness of the panel. Also in a continuous pressing operation the rate of temperature rise coordinated with the rate of pressure application can be used to change the density profile with thickness to the panel.
It is economical to product wafers since the wafers are normally produced by a blade having spaced edges equal in length to the length of the wafer to be produced cutting substantially parallel to the grain. In some cases flat blades cutting parallel to the grain are used with spaced spurs cutting perpendicular to the grain to define the length of the wafers. Wafers so produced are generally relatively thin and have a width many times greater than their thickness (thickness being determined by the depth of cut of the blade and the width being determined by the deflection of the cut wafer by the breaker bar of the knife).